How does blue light affect circadian rhythm?

Blue light suppresses the body's secretion of melatonin, a hormone that regulates circadian rhythms and induces sleep^[1]. While all forms of visible light can affect circadian timing, short-wavelength blue light has the most powerful impact^[2]. Research shows that evening exposure to blue light can suppress melatonin for about twice as long as green light of comparable brightness and shift circadian rhythms by twice as much, effectively tricking the brain into thinking it is still daytime^[3][4] This disruption leads to difficulties falling asleep, reduced sleep quality, and decreased deep sleep^[5][6]

Mitigation strategies focus on managing light exposure timing and filtering:
- Timing and Reduction: The most effective approach is turning off screens and reducing bright LED or fluorescent lighting two to three hours before bedtime^[7][8]
- Software Filters and Dark Mode: Applications, dark mode settings, and night-mode features adjust screen color temperatures or lower luminance, though studies note that software filters alone provide modest reductions in ipRGC-stimulating light and work best when paired with reduced overall brightness^[9][10]
- Eyewear: Amber-tinted or specialized blue-blocking glasses can block short-wavelength light and help prevent evening melatonin suppression when using electronic devices^[11][12]
- Daytime Habits: Exposing yourself to bright natural light during the day strengthens your circadian rhythm and makes the evening transition more effective^[13][14][15]